Effect Of Biochar-treated Soil And Its Aging On The Adsorption Of Heavy Metals And Phthalates

With the rapid development of industry and agriculture,large areas of farmland soils were polluted by heavy metals and organic contaminants,which have raised widely public concerns in recent years.On one hand,the unreasonable mining activities and discharge of industrial wastes have lead to heavy metals accumulations in soils.On the other hand,the overuse of organic fertilizers,pesticides and plastic products(e.g.mulching film)resulted in soil organic pollution.Diethyl phthalate(DEP),as the most commonly used plasticizer compound,is one of the typical phthalate esters in soil.At present,the areas of soil co-contaminated with heavy metals and phthalate esters have expanded rapidly.Biochar is considered as a highly effective soil amendment which has potential to remediate the soils contaminated with heavy metals or organic contaminants.Therefore,this study simulated the nature aging process of biochar in soil,the fresh and aged biochar was characterized and the aged biochar-treated soil physicochemical properties were measured.Meanwhile,cadmium(Cd),zinc(Zn)and DEP were selected to investigate the adsorption behavior in soils under different biochar application and aging process.The aim of this study was to provide a theoretical basis for further improving the remediation effect of biochar on co-contaminated soil.The main research results are as following:1.Due to the difference of raw materials,the surface characteristics and basic physicochemical properties of the pig and P.orientalis biochar were obviously different.The animal-derived biochar(Pig biochar)had higher pH,electrical conductivity(EC),surface alkalinity,ash content,mineral elements and surface functional groups than P.orientalis biochar,and was more prominent on improving soil pH,EC and cation exchange capacity(CEC).And the plant-derived biochar(P.orientalis biochar)had abundant carbon content,and thereby was more effective on increasing soil total organic carbon content(TOC).With the increase of biochar application rates,the biochar-treated soil pH,EC and TOC were increased significantly(P<0.05).2.During the 6-month natural aging process,the kinds of oxygen-containing functional groups on biochar surface were increased.The SEM spectra indicated that the organo-mineral micro-agglomerates were observed on biochar microspores.The FTIR spectra showed that hydroxyl(-OH)and ethers(C-O-C)absorption peak vibration in pig biochar,the ethers(C-O-C)and carboxyl(C=O)absorption peak vibration in P.orientalis biochar were strengthened.XPS spectra showed that the content of C-O-and C=O in both biochars increased.In addition,compared to the fresh biochar treatments,the biochar-treated soil pH,CEC and TOC were on the rise after aging for 1 month,while the EC of the biochar-treated soil with low organic carbon contents was decreased.After aging for 6 months,the biochar-treated soil EC,CEC and TOC showed a general trend of decline,but the soil pH was still significantly(P<0.05)increased.3.Langmuir model was better to describe the adsorption process of Cd,Zn in different aged biochar-treated soils.(1)The biochar-treated soil with high organic carbon content had stronger adsorption capacity for Cd and Zn than soil with low organic carbon content.The adsorption capacity of pig biochar-treated soil for Cd and Zn was stronger than P.orientalis biochar treatments,and the biochar effect was application rate responsive.(2)In the process of natural aging,the adsorption of Cd and Zn in biochar-treated soils basically increased in 1-month aging treatments,decreased in 6-month aging treatments.In general,the adsorption capacity of 1-month and 6-month aged bicohar-treated soil to Zn and Cd was stronger than that of the fresh biochar-treated soil.(3)DEP in the solution could promote the adsorption capacity of Zn and Cd in fresh biochar-treated soil,but inhibited the adsorption capacity of Zn and Cd in aged biochar-treated soil.4.Freundlich model was more suitable to describe the adsorption process of DEP in biochar-treated soil.(1)The pig biochar-treated soil with high organic carbon content had greater capacity for DEP adsorption than other biochar-treated soils.In the adsorption process of DEP,physical adsorption was the dominant process of biochar-treated soil with low organic matter,while distribution is the dominant process of biochar-treated soil with high organic carbon.(2)Compared to fresh biochar-treated soil,the adsorption capacity of DEP on aged biochar-treated soil decreased,and its adsorption capacity decreased with the extension of aging time.(3)The presence of Zn,Cd would decrease the adsorption capacity of DEP in the aged biochar-treated soil.In conclusion,pig biochar is more efficient than P.orientalis biochar in improving soil physicochemical properties and adsorption capacity of Zn,Cd or DEP in soil.After a short period of natural aging,the surface oxygen-containing functional groups of both biochar increased,the basic physicochemical properties of biochar-treated soil improved,which was conducive to the adsorption of heavy metals,inhibiting the adsorption of phthalate esters.The presence of DEP could promote the biochar-treated soil adsorption of Cd and Zn,and the presence of Cd and Zn inhibited the biochar-treated soil adsorption effect of DEP.